Studies conducted on canine SLE in an established breeding colony have demonstrated the presence of a transmissible agent capable of inducing the serologic abnormalities of SLE in normal mice and puppies and of activating latent murine leukemia virus in mice. The objectives of this proposal are five fold: a. to isolate and identify the canine lupus virus; b. to relate this agent to the cause of SLE in dogs; c. to apply to human SLE the system used in the study of a transmissible agent in canine SLE; d. to clarify the interactions between the agent associated with canine SLE and murine RNA leukemia viruses; e. to continue development of the inbred SLE dog colony. The methods employed in this proposal include: in vivo bioassay of cell free material from affected individuals; in vitro tissue culture techniques, including long term cell lines as well as short term mixed cell cultures; isopycnic separation of viruses and viral nucleic acids; electronmicroscopy; fluorescent and phase microscopy; and conventional immunologic techniques.